Age differences in the speed with which children, adolescents, and adults execute mental processes are ubiquitous and large. Furthermore, age differences in processing speed often affect other cognitive processes directly and indirectly, via working memory. Understanding the nature and consequences of these age differences is the general goal of the proposed work. Three specific aims follow from this goal: [unreadable] [unreadable] 1. Most of the evidence concerning change in processing speed comes from cross-sectional studies; relatively little is known about growth of processing speed in individuals. A proposed longitudinal study will provide evidence concerning the nature of growth of processing speed in individuals during childhood and adolescence. [unreadable] [unreadable] 2. Evidence regarding the consequences of age-related change in processing speed it is based largely on cross-sectional analyses of correlations between processing speed and other cognitive processes. The proposed longitudinal study is designed to provide stronger evidence for the cognitive consequences of developmental change in processing speed. [unreadable] [unreadable] 3. Cognitive development reflects both processes that are global (e.g., processing speed, working memory) as well as processes specific to particular domains of knowledge. Nevertheless, there is little research that addresses the contributions of both global and domain-specific processes within a single task or domain. Four studies are proposed that would reveal how the indirect and direct effects of age-related change in processing speed interact with domain-specific processes to yield cognitive change. [unreadable] [unreadable]